Metrology tool, system comprising a lithographic apparatus and a metrology tool, and a method for determining a parameter of a substrate

ABSTRACT

A metrology tool is arranged to measure a parameter of a substrate that has been provided with a pattern in a lithographic apparatus. The metrology tool includes a base frame, a substrate table constructed and arranged to hold the substrate, at least one sensor constructed and arranged to measure a parameter of the substrate, a displacement system to displace one of the substrate table and sensor with respect to the other one of the substrate table and sensor in at least a first direction, a first balance mass, and a first bearing which movably supports the first balance mass so as to be substantially free to translate in the opposite direction of the first direction in order to counteract a displacement of the one of the substrate table and sensor in the first direction.

FIELD OF THE INVENTION

The present invention relates to a metrology tool for measuring aparameter of a substrate which substrate has been provided with apattern in a lithographic apparatus, the parameter for example being anOverlay (Ovl) and/or Critical Dimensions (CD) and/or Film Thickness (FT)and/or Refractive Index (RI) of a layer. The invention also relates to asystem comprising a lithographic apparatus and a metrology tool, as wellas a method for determining said parameter of a substrate coming from alithographic apparatus.

DESCRIPTION OF THE RELATED ART

A track is a machine that applies one or more photosensitive films ontoa substrate (zero or more films may be anti-reflective coatings toimprove imaging performance of the lithographic apparatus). Thethickness and refractive index of each film may be critical and musttherefore be controlled e.g. using FT and/or RI measurements.

This coated substrate can be measured using the metrology tool, data isprocessed and can be used for feedback or feed forward control ofupstream and downstream process steps.

The coated substrate is now transported to the lithographic apparatusfor exposure.

A lithographic apparatus is a machine that applies a desired patternonto a substrate, usually onto a target portion of the substrate. Alithographic apparatus can be used, for example, in the manufacture ofintegrated circuits (ICs). In such a case, a patterning device, which isalternatively referred to as a mask or a reticle, may be used togenerate a circuit pattern to be formed on an individual layer of theIC. This pattern can be transferred onto a target portion (e.g.including part of, one, or several dies) on a substrate (e.g. a siliconwafer). Transfer of the pattern is typically via imaging onto a layer ofradiation-sensitive material (resist) provided on the substrate. Ingeneral, a single substrate will contain a network of adjacent targetportions that are successively patterned. Conventional lithographicapparatus include so-called steppers, in which each target portion isirradiated by exposing an entire pattern onto the target portion atonce, and so-called scanners, in which each target portion is irradiatedby scanning the pattern through a radiation beam in a given direction(the “scanning”-direction) while synchronously scanning the substrateparallel or anti-parallel to this direction. It is also possible totransfer the pattern from the patterning device to the substrate byimprinting the pattern onto the substrate.

In the lithographic apparatus it is critical to accurately set theposition of the substrate, in order to position different layerscorrectly on top of each other. This process is known as aligning.Accurate aligning is generally done by accurately determining theposition of the substrate relative to a substrate table and determiningthe position of the substrate table with respect to the mask andprojection beam. With this it is possible to use different alignmentstrategies. Choosing the optimal alignment strategy is important inobtaining optimal overlay. Different procedures for selecting analignment strategy have been developed to comply with differentapplications. With this use is being made of an overlay indicator. Seefor further description of possible alignment strategies for instanceU.S. Pat. No. 7,042,552, which is incorporated herein by reference.

Besides overlay the shape “Critical Dimensions” of the exposedstructures (like lines and/or contact holes) is an important parameterto control.

After exposure the substrate is developed, the exposed or unexposedresist is removed (depending on positive or negative resist). The shapeof the formed resist structures must be correct, in OVL, CD, etc. thisis checked using a metrology tool after the develop process.

The values of the overlay indicators can for example be calculated bymeasuring single batches of substrates on an overlay metrology tool. Forthis an offline overlay metrology tool is used in order to get highconfidence values. Measuring of the substrates on the offline overlaymetrology tool causes extra effort and time, particularly since theoverlay metrology tool is relatively slow, due to low speed stages andbecause of high settling times.

Competing metrology tools have relatively high acquisition times suchthat lower move times do not impact throughput greatly. In case of ametrology tool with low acquisition times the movement time becomes thedominant throughput limiter. Fast stages with low (system) settlingtimes become important.

A measurement (Move-Acquire-Measure) consists of:

move to a measurement site on the wafer, this site has specialstructures (including no structure at all for FT or structures inmultiple process layers) to be sensitive for the effect(s) beinginvestigated (like Ovl, CD, FT, RI etc.)

acquisition: illuminating the site with light of certain wavelength (andcertain bandwidth), certain polarization mode and aperture settings. Thereflected light is projected on a sensor.

Measurement: the sensor data is processed using certain algorithms toyield information on the effects that must be reported (OVL, CD, FT,RI).

SUMMARY

It is desirable to provide a high speed metrology tool for measuring aparameter of a substrate, which substrate has been provided with apattern in a lithographic apparatus.

According to an embodiment of the invention there is provided ametrology tool arranged to measure a parameter of a substrate whichsubstrate has been provided with a pattern in

a lithographic apparatus, said metrology tool comprising:

a base frame;

a substrate table constructed and arranged to hold the substrate;

at least one sensor constructed and arranged to measure a parameter ofthe substrate;

a displacement system for displacing one of the substrate table andsensor with respect to the other one in at least a first direction;

a first balance mass;

a first bearing which movably supports the first balance mass so as tobe substantially free to translate in the opposite direction of thefirst direction in order to counteract a displacement of said one of thesubstrate table and sensor in said first direction.

In another embodiment of the invention there is provided a systemcomprising:

a lithographic apparatus comprising:

an illumination system configured to condition a radiation beam;

a support constructed to support a patterning device, the patterningdevice being capable of imparting the radiation beam with a pattern inits cross-section to form a patterned radiation beam;

a substrate table constructed to hold a substrate; and

a projection system configured to project the patterned radiation beamonto a target portion of the substrate;

a metrology tool according to the present invention; and

transfer means for transferring substrates from the lithographicapparatus to the metrology tool.

According to a further embodiment of the invention there is provided amethod for determining a parameter of a substrate, comprising the steps:

providing a substrate with a pattern in a lithographic apparatus;transferring the substrate from the lithographic apparatus to asubstrate table of a metrology tool; and

measuring a parameter of the substrate inside the metrology tool with asensor; during which measuring, one of the substrate table and sensor isdisplaced with respect to the other one in at least a first direction,which displacement is counteracted with a translation of a balance massin the opposite direction.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying schematic drawings in whichcorresponding reference symbols indicate corresponding parts, and inwhich:

FIG. 1 depicts a lithographic apparatus according to the state of theart;

FIG. 2 depicts a system according to an aspect of the invention;

FIG. 3 a depicts a metrology tool according to the state of the art;

FIG. 3 b depicts the metrology tool of FIG. 3 a without the base frame;

FIG. 4 depicts a part of the metrology tool of FIG. 3 showing anembodiment of a substrate table with passive balance mass systemaccording to the invention;

FIG. 5 depicts an embodiment corresponding to FIG. 4 with an activebalance mass system according to the invention;

FIG. 6 depicts an embodiment corresponding to FIG. 5 with the balancemass system coupled indirectly to the substrate table; and

FIG. 7 shows an embodiment corresponding to FIG. 4 with a balance masssystem in line with the substrate table.

DETAILED DESCRIPTION

FIG. 1 schematically depicts a lithographic apparatus. The apparatusincludes an illumination system (illuminator) IL configured to conditiona radiation beam B (e.g. UV radiation or any other suitable radiation),a mask support structure (e.g. a mask table) MT constructed to support apatterning device (e.g. a mask) MA and connected to a first positioningdevice PM configured to accurately position the patterning device inaccordance with certain parameters. The apparatus also includes asubstrate table (e.g. a wafer table) WT or “substrate support”constructed to hold a substrate (e.g. a resist-coated wafer) W andconnected to a second positioning device PW configured to accuratelyposition the substrate in accordance with certain parameters. Theapparatus further includes a projection system (e.g. a refractiveprojection lens system) PS configured to project a pattern imparted tothe radiation beam B by patterning device MA onto a target portion C(e.g. including one or more dies) of the substrate W.

The illumination system may include various types of optical components,such as refractive, reflective, magnetic, electromagnetic, electrostaticor other types of optical components, or any combination thereof, fordirecting, shaping, or controlling radiation.

The mask support structure supports, i.e. bears the weight of, thepatterning device. It holds the patterning device in a manner thatdepends on the orientation of the patterning device, the design of thelithographic apparatus, and other conditions, such as for examplewhether or not the patterning device is held in a vacuum environment.The mask support structure can use mechanical, vacuum, electrostatic orother clamping techniques to hold the patterning device. The masksupport structure may be a frame or a table, for example, which may befixed or movable as required. The mask support structure may ensure thatthe patterning device is at a desired position, for example with respectto the projection system. Any use of the terms “reticle” or “mask”herein may be considered synonymous with the more general term“patterning device.”

The term “patterning device” used herein should be broadly interpretedas referring to any device that can be used to impart a radiation beamwith a pattern in its cross-section so as to create a pattern in atarget portion of the substrate. It should be noted that the patternimparted to the radiation beam may not exactly correspond to the desiredpattern in the target portion of the substrate, for example if thepattern includes phase-shifting features or so called assist features.Generally, the pattern imparted to the radiation beam will correspond toa particular functional layer in a device being created in the targetportion, such as an integrated circuit.

The patterning device may be transmissive or reflective. Examples ofpatterning devices include masks, programmable mirror arrays, andprogrammable LCD panels. Masks are well known in lithography, andinclude mask types such as binary, alternating phase-shift, andattenuated phase-shift, as well as various hybrid mask types. An exampleof a programmable mirror array employs a matrix arrangement of smallmirrors, each of which can be individually tilted so as to reflect anincoming radiation beam in different directions. The tilted mirrorsimpart a pattern in a radiation beam which is reflected by the mirrormatrix.

The term “projection system” used herein should be broadly interpretedas encompassing any type of projection system, including refractive,reflective, catadioptric, magnetic, electromagnetic and electrostaticoptical systems, or any combination thereof, as appropriate for theexposure radiation being used, or for other factors such as the use ofan immersion liquid or the use of a vacuum. Any use of the term“projection lens” herein may be considered as synonymous with the moregeneral term “projection system”.

As here depicted, the apparatus is of a transmissive type (e.g.employing a transmissive mask). Alternatively, the apparatus may be of areflective type (e.g. employing a programmable mirror array of a type asreferred to above, or employing a reflective mask).

The lithographic apparatus may be of a type having two (dual stage) ormore substrate tables or “substrate supports” (and/or two or more masktables or “mask supports”). In such “multiple stage” machines theadditional tables or supports may be used in parallel, or preparatorysteps may be carried out on one or more tables or supports while one ormore other tables or supports are being used for exposure.

The lithographic apparatus may also be of a type wherein at least aportion of the substrate may be covered by a liquid having a relativelyhigh refractive index, e.g. water, so as to fill a space between theprojection system and the substrate. An immersion liquid may also beapplied to other spaces in the lithographic apparatus, for example,between the mask and the projection system. Immersion techniques can beused to increase the numerical aperture of projection systems. The term“immersion” as used herein does not mean that a structure, such as asubstrate, must be submerged in liquid, but rather only means that aliquid is located between the projection system and the substrate duringexposure.

Referring to FIG. 1, the illuminator IL receives a radiation beam from aradiation source SO. The source and the lithographic apparatus may beseparate entities, for example when the source is an excimer laser. Insuch cases, the source is not considered to form part of thelithographic apparatus and the radiation beam is passed from the sourceSO to the illuminator IL with the aid of a beam delivery system BDincluding, for example, suitable directing mirrors and/or a beamexpander. In other cases the source may be an integral part of thelithographic apparatus, for example when the source is a mercury lamp.The source SO and the illuminator IL, together with the beam deliverysystem BD if required, may be referred to as a radiation system.

The illuminator IL may include an adjuster AD configured to adjust theangular intensity distribution of the radiation beam. Generally, atleast the outer and/or inner radial extent (commonly referred to asσ-outer and σ-inner, respectively) of the intensity distribution in apupil plane of the illuminator can be adjusted. In addition, theilluminator IL may include various other components, such as anintegrator IN and a condenser CO. The illuminator may be used tocondition the radiation beam, to have a desired uniformity and intensitydistribution in its cross-section.

The radiation beam B is incident on the patterning device (e.g., maskMA), which is held on the mask support structure (e.g., mask table MT),and is patterned by the patterning device. Having traversed the mask MA,the radiation beam B passes through the projection system PS, whichfocuses the beam onto a target portion C of the substrate W. With theaid of the second positioning device PW and position sensor IF (e.g. aninterferometric device, linear encoder or capacitive sensor), thesubstrate table WT can be moved accurately, e.g. so as to positiondifferent target portions C in the path of the radiation beam B.Similarly, the first positioning device PM and another position sensor(which is not explicitly depicted in FIG. 1) can be used to accuratelyposition the mask MA with respect to the path of the radiation beam B,e.g. after mechanical retrieval from a mask library, or during a scan.In general, movement of the mask table MT may be realized with the aidof a long-stroke module (coarse positioning) and a short-stroke module(fine positioning), which form part of the first positioning device PM.Similarly, movement of the substrate table WT or “substrate support” maybe realized using a long-stroke module and a short-stroke module, whichform part of the second positioner PW. In the case of a stepper (asopposed to a scanner) the mask table MT may be connected to ashort-stroke actuator only, or may be fixed. Mask MA and substrate W maybe aligned using mask alignment marks M1, M2 and substrate alignmentmarks P1, P2. Although the substrate alignment marks as illustratedoccupy dedicated target portions, they may be located in spaces betweentarget portions (these are known as scribe-lane alignment marks).Similarly, in situations in which more than one die is provided on themask MA, the mask alignment marks may be located between the dies.

The depicted apparatus could be used in at least one of the followingmodes:

1. In step mode, the mask table MT or “mask support” and the substratetable WT or “substrate support” are kept essentially stationary, whilean entire pattern imparted to the radiation beam is projected onto atarget portion C at one time (i.e. a single static exposure). Thesubstrate table WT or “substrate support” is then shifted in the Xand/or Y direction so that a different target portion C can be exposed.In step mode, the maximum size of the exposure field limits the size ofthe target portion C imaged in a single static exposure.

2. In scan mode, the mask table MT or “mask support” and the substratetable WT or “substrate support” are scanned synchronously while apattern imparted to the radiation beam is projected onto a targetportion C (i.e. a single dynamic exposure). The velocity and directionof the substrate table WT or “substrate support” relative to the masktable MT or “mask support” may be determined by the (de-)magnificationand image reversal characteristics of the projection system PS. In scanmode, the maximum size of the exposure field limits the width (in thenon-scanning direction) of the target portion in a single dynamicexposure, whereas the length of the scanning motion determines theheight (in the scanning direction) of the target portion.

3. In another mode, the mask table MT or “mask support” is keptessentially stationary holding a programmable patterning device, and thesubstrate table WT or “substrate support” is moved or scanned while apattern imparted to the radiation beam is projected onto a targetportion C. In this mode, generally a pulsed radiation source is employedand the programmable patterning device is updated as required after eachmovement of the substrate table WT or “substrate support” or in betweensuccessive radiation pulses during a scan. This mode of operation can bereadily applied to maskless lithography that utilizes programmablepatterning device, such as a programmable mirror array of a type asreferred to above.

Combinations and/or variations on the above described modes of use orentirely different modes of use may also be employed.

FIG. 2 shows an example of a system comprising a lithographic apparatus1, a metrology tool 2 and a processor 3. The lithographic apparatus 1may for example be constructed according to the embodiment shown inFIG. 1. The metrology tool 2 is arranged to measure a parameter of asubstrate coming from the lithographic apparatus 1, e.g. overlay ofpatterns provided on substrates into the lithographic apparatus. Theprocessor 3 is constructed and arranged to receive parameter data fromthe metrology tool 2 and alignment data from the lithographic apparatus1. The processor 3 may be part of the lithographic apparatus, but otherconfigurations are possible. The parameter data may be received by theprocessor 3 directly from the metrology tool 2 or from an attachedsoftware application, loaded on another processor, not shown, or on thesame processor 3. Preferably the system is arranged in a computernetwork such as to communicate with other apparatus and/or applications.

During manufacturing processes with the lithographic apparatus 1,substrates may be grouped in a box to form a particular batch.Substrates in such a batch stay together throughout the entiremanufacturing process. The batches pass several manufacturing actions.The main manufacturing actions (but not limited to) which are ofinterest for this invention, are lithographic exposure actions in thelithographic apparatus 1 and an inspection action, e.g. an overlayinspection action, in the metrology tool 2 and etch.

The overlay data may, for example, be determined by measuring positionerrors for a plurality of overlay targets present on each of theselected substrates. This will result in so-called measured overlaydata. Next, the overlay data may be processed.

FIG. 3 shows an embodiment according to the state of the art of themetrology tool 2. The metrology tool 2 comprises a base frame 5. Withthe base frame 5 a wafer stage 6 is movably connected in the y-directionwith respect to the base frame 5 by means of a first displacementsystem. Above the wafer stage 6 a sensor 7 is provided. The sensor 7forms part of a sensor stage 8 which is movably connected in thex-direction with respect to the base frame 5 by means of a seconddisplacement system. The wafer stage 6 is constructed to hold asubstrate 9. For this the wafer stage 6 comprises a wafer table 10. Thewafer stage 6 is provided with a third displacement system for rotatingthe wafer table 10 around the z-axis with respect to the wafer stage 6.

Thus the wafer 9 and the sensor 7 can be moved with respect to eachother in several directions, which makes it possible to measure forexample the entire overlay of patterns on the wafer 9 when held on thewafer table 10 of the wafer stage 6.

Furthermore the metrology tool 2 comprises transfer means in the form ofa wafer exchanger gripper 15, which can be seen in FIG. 3 b.

In the metrology tool 2, reactions on the base frame 5, accelerationforces used to position the wafer table 10 and sensor 7 tosub-micrometer accuracy, are a major cause of vibrations. Thesevibrations impair the accuracy of the metrology tool 2. To minimize theeffects of the vibrations, according to the state of the art theacceleration forces of the stages 6, 8 and/or table 10 are kept as lowas possible, and/or the base frame 5 of the metrology tool 2 is keptisolated from the lithographic apparatus 1. Otherwise the vibrationscoming from the metrology tool 2 would impair the accuracy of thelithographic process in the lithographic apparatus 1.

In order to be able to move the wafer stage 6 and/or wafer table 10 withthe wafer 9 and the sensor stage 8 with the sensor 7 at higher speedwith respect to each other, the present invention provides for the useof balance masses in the metrology tool (not shown in FIG. 3). Thus afirst balance mass may be constructed and arranged to counteractdisplacements of the sensor stage 8 with the sensor 7 in the x-directionwith respect to the base frame 5. In addition and/or as an alternative asecond balance mass may be constructed and arranged to counteractdisplacements of the wafer stage 6 with the wafer table 10 and the wafer9 in the y-direction with respect to the base frame 5. In additionand/or as an alternative a third balance mass may be constructed andarranged to counteract displacements of the wafer table 10 and the wafer9 around the z-direction with respect to the wafer stage 6 and baseframe 5.

As a non-limitative example, in FIGS. 4-7, embodiments are shown forproviding a balance mass system for the movability of the wafer stage 6with wafer table 10 and wafer 9 in the y-direction. Similar systems mayalso be provided for counteracting displacements of the sensor stage 8with sensor 7 and/or of the wafer table 10 with wafer 9.

In FIG. 4 a balance mass 20 is provided, which is placed on a bearing 21(for example a roller bearing or air bearing). The bearing 21 movablysupports the balance mass 20 with respect to the base frame 5 so as tobe substantially free to translate in a direction which is opposite to adisplacement of the wafer stage 6 with wafer table 10 and wafer 9 in they-direction. The balance mass 20 is coupled to the wafer stage 6 bymeans of a wafer stage positioning actuator 25, for example a steppingmotor or other steerable drive. The wafer stage 6 is placed on a bearing27. The bearing 27 movably supports the wafer stage 6 with respect tothe balance mass 20 so as to be substantially free to be displaced inthe y-direction by the actuator 25.

The balance mass 20 is coupled to the base frame 5 via an elasticcoupling comprising a spring 30. Furthermore the balance mass 20 iscoupled to the base frame 5 via a damper 31. The damper 31 is positionedin parallel with the spring 30.

Between the balance mass 20 and the base frame 5 a feed forwardcontroller 33 is provided, which measured the position of the balancemass 20 with respect to the base frame 5. Such a feed forward controlleris also provided between the wafer stage 6 and the balance mass 20,which feed forward controller is given the reference numeral 35.

If, during measurement of the overlay of the substrate 9, the waferstage 6 is driven by the actuator 25, and thus displaced in they-direction, a reaction force is immediately set on the balance mass 20,causing the balance mass 20 to move in the opposite direction. Theamount of displacement of the balance mass in the opposite directiondepends on the mass ratio of the balance mass 20 with respect to thewafer stage 6 (including the wafer table 10, the wafer 9, etc.). Withthis the spring 30 and damper 31 are used to damp movement of thebalance mass to avoid wind up, that is to say resonance of the balancemass. The provision of this balance mass system makes it possible tosubstantially enlarge the speed and acceleration forces of the waferstage 6. The higher speed and higher acceleration forces no longer leadto vibrations and/or other disturbing forces in the base frame 5 of themetrology tool 2. This in turn makes it possible position the metrologytool at any desired position with respect to the lithographic apparatus.For example the metrology tool with the balance mass system according tothe present invention may now be placed even on top of an existinglithographic apparatus or at least connected therewith.

FIG. 5 shows a variant embodiment of FIG. 4 in which the spring-dampersystem between the balance mass 20 and the base frame 5 is replaced by abalance mass positioning actuator 50, for example a stepping motor orother steerable drive. If in this embodiment the wafer stage 6 isdisplaced in the y-direction by proper steering of the wafer stagepositioning actuator 25, this is immediately detected by the feedforward controller 35 which sends out a signal to the balance masspositioning actuator 50 in order to displace the balance mass 20 by acorresponding amount in the opposite direction. In order to be able toproperly steer the wafer stage positioning actuator 25 and the balancemass positioning actuator 50, the feed forward controller 33 is used.The balance mass actuator 50 may also be used to correct the position ofthe balance mass 20 which can have a tendency to drift from a correctposition. This drift, can be the result of friction between the baseframe 5 and the balance mass 20, for example.

FIG. 6 shows a variant embodiment of FIG. 5, in which the wafer stage 6is supported with its bearing 27 directly on the base frame 5. Thebalance mass 20 itself is also supported with its bearing 21 directly onthe base frame 5. The wafer stage 6 is now directly connected with itswafer stage positioning actuator 25 and its feed forward controller 35to the base frame 5. The balance mass 20 is also directly connected withits balance mass positioning actuator 50 and its feed forward controller33 to the base frame 5. During measurement of for example the overlay ofthe wafer 9, a displacement of the wafer stage 6 by means of thepositioning actuator 25 is detected by the feed forward controller 35which sends out a signal to the balance mass positioning actuator 50 inorder to displace the balance mass 20 in the opposite direction by anappropriate amount.

FIG. 7 shows a variant embodiment of FIG. 4, in which the wafer stage 6is supported with its bearing 27 directly on the base frame 5. Thebalance mass 20 itself is also supported with its bearing 21 directly onthe base frame 5. The wafer stage 6 and the balance mass 20 arepositioned in line with each other. The wafer stage 6 is now directlyconnected with its wafer stage positioning actuator 25 to the balancemass 20, and with its feed forward controller 35 to the base frame 5.The balance mass 20 is directly connected with its spring 30 and itsdamper 31 to the base frame 5.

Besides the embodiments shown many variants are possible. Instead ofwafers other types of substrates may be used. For example more than onesensor may be provided in the metrology tool. The sensor stage or thewafer stage of the metrology tool may also be moveably coupled with thebase frame in both the x and y-direction, while the other one of thesensor stage and the wafer stage being fixedly connected with the baseframe. Important is that in the metrology tool the substrate and the oneor more sensors are moveable with respect to each other which movementsare counteracted with opposite movements of balance masses. In thismanner each point of the wafer can be measured efficient and without(causing) vibrations. Another example of a metrology tool including abalance mass system, is that at least one of the stages is build as astage carrying coils (rotor) to generate a varying magnetic field movingover a plate with static magnets (stator). The rotor is guided and canmove with respect to the stator. The stator can move with respect to aguidance. It the rotor is accelerated to the left, the stator will moveto the right due to the reaction forces. The center of gravity of therotor and stator together can thus remain at the same position(neglecting friction forces, etc.). If the stage drifts away whenmultiple moves are performed, then in a variant embodiment it is alsopossible to use two weak springs mounted on either side (in thedisplacement direction) of the stator to the base frame as a balancemass compensator. Another embodiment of an active balance masscompensator is a controlled actuator with sufficient stroke. The balancemass is typically, but not necessarily, heavier than the one of thesubstrate stage or the sensor stage (including their payload) of whichthe displacement needs to be compensated. The metrology tool can beintegrated into a lithographic system (like a track, scanner or etcher).It can also be mounted separately thereon, or be constructed andarranged as a stand-alone unit. Most likely the metrology tool is placed“in-line” with a lithographic apparatus. The metrology tool can also beintegrated into an etcher. This process removes material, which is notprotected by the (remaining) resist film. This process ‘copies’ theexposed features into the layer(s) of material below the resist film(s).

Although specific reference may be made in this text to the use oflithographic apparatus in the manufacture of ICs, it should beunderstood that the lithographic apparatus described herein may haveother applications, such as the manufacture of integrated opticalsystems, guidance and detection patterns for magnetic domain memories,flat-panel displays, liquid-crystal displays (LCD's), thin-film magneticheads, etc. The skilled artisan will appreciate that, in the context ofsuch alternative applications, any use of the terms “wafer” or “die”herein may be considered as synonymous with the more general terms“substrate” or “target portion”, respectively. The substrate referred toherein may be processed, before or after exposure, in for example atrack (a tool that typically applies a layer of resist to a substrateand develops the exposed resist), a metrology tool and/or an inspectiontool. Where applicable, the disclosure herein may be applied to such andother substrate processing tools. Further, the substrate may beprocessed more than once, for example in order to create a multi-layerIC, so that the term substrate used herein may also refer to a substratethat already contains multiple processed layers.

Although specific reference may have been made above to the use ofembodiments of the invention in the context of optical lithography, itwill be appreciated that the invention may be used in otherapplications, for example imprint lithography, and where the contextallows, is not limited to optical lithography. In imprint lithography atopography in a patterning device defines the pattern created on asubstrate. The topography of the patterning device may be pressed into alayer of resist supplied to the substrate whereupon the resist is curedby applying electromagnetic radiation, heat, pressure or a combinationthereof. The patterning device is moved out of the resist leaving apattern in it after the resist is cured.

The terms “radiation” and “beam” used herein encompass all types ofelectromagnetic radiation, including ultraviolet (UV) radiation (e.g.having a wavelength of or about 365, 248, 193, 157 or 126 nm) andextreme ultra-violet (EUV) radiation (e.g. having a wavelength in therange of 5-20 nm), as well as particle beams, such as ion beams orelectron beams.

The term “lens”, where the context allows, may refer to any one orcombination of various types of optical components, includingrefractive, reflective, magnetic, electromagnetic and electrostaticoptical components.

While specific embodiments of the invention have been described above,it will be appreciated that the invention may be practiced otherwisethan as described. For example, the invention may take the form of acomputer program containing one or more sequences of machine-readableinstructions describing a method as disclosed above, or a data storagemedium (e.g. semiconductor memory, magnetic or optical disk) having sucha computer program stored therein.

The descriptions above are intended to be illustrative, not limiting.Thus, it will be apparent to one skilled in the art that modificationsmay be made to the invention as described without departing from thescope of the claims set out below.

1. A metrology tool arranged to measure a parameter of a substrate whichsubstrate has been provided with a pattern in a lithographic apparatus,said metrology tool comprising: a base frame; a substrate tableconstructed and arranged to hold the substrate; at least one sensorconstructed and arranged to measure a parameter of the substrate; adisplacement system for displacing one of the substrate table and sensorwith respect to the other one in at least a first direction; a firstbalance mass; a first bearing which movably supports the first balancemass so as to be substantially free to translate in the oppositedirection of the first direction in order to counteract a displacementof said one of the substrate table and sensor in said first direction.2. A metrology tool according to claim 1, wherein the balance mass iscoupled to said one of the substrate table and sensor.
 3. A metrologytool according to claim 2, wherein a positioning actuator couples thebalance mass with said one of said substrate table and sensor.
 4. Ametrology tool according to claim 1, wherein said one of the substratetable and sensor is movably supported on a second bearing so as to besubstantially free to be displaced in the first direction by thedisplacement system.
 5. A metrology tool according to claim 4, whereinthe second bearing is provided between the balance mass and said one ofthe substrate table and sensor.
 6. A metrology tool according to claim1, wherein the balance mass is coupled to the base frame via an elasticcoupling.
 7. A metrology tool according to claim 6, wherein the elasticcoupling comprises a spring.
 8. A metrology tool according to claim 1,wherein the balance mass is coupled to the base frame via a damper.
 9. Ametrology tool according to claim 1, wherein the balance mass is coupledto the base frame via a spring-damper system comprises at least oneelement having the characteristics of a spring connected in series withat least one element having the characteristics of a damper.
 10. Ametrology tool according to claim 1, wherein the balance mass is coupledto the base frame via an elastic coupling and a damper positioned inparallel with the elastic coupling.
 11. A metrology tool according toclaim 1, further comprising a feed forward controller constructed andarranged to measure the position of said one of the substrate table andsensor with respect to the balance mass and/or base frame.
 12. Ametrology tool according to claim 1, further comprising a feed forwardcontroller constructed and arranged to measure the position of thebalance mass with respect to the base frame.
 13. A metrology toolaccording to claim 1, further comprising a balance mass positioningactuator constructed and arranged to control the position of the balancemass.
 14. A metrology tool according to claim 13, wherein the balancemass is coupled to the base frame via the balance mass actuator.
 15. Ametrology tool according to claim 1, wherein said one of the substratetable and sensor is coupled to the base frame via a positioning actuatorand a feed forward controller, and wherein the balance mass is coupledto the base frame via a balance mass actuator and a feed forwardcontroller.
 16. A metrology tool according to claim 1, wherein the firstbearing is provided between the balance mass and the base frame.
 17. Ametrology tool according to claim 1, wherein the balance mass isprovided in line with said one of the substrate table and sensor.
 18. Ametrology tool according to claim 1, wherein the displacement system isalso constructed and arranged for displacing one of the substrate tableand sensor with respect to the other one in a second directionperpendicular to the first direction, wherein a second balance mass isprovided, and wherein a third bearing is provided which movably supportsthe second balance mass so as to be substantially free to translate inthe opposite direction of the second direction in order to counteract adisplacement of said one of the substrate table and sensor in saidsecond direction.
 19. A metrology tool according to claim 1, wherein thedisplacement system is also constructed and arranged for displacing oneof the substrate table and sensor with respect to the other one in athird direction which is a rotational direction, wherein a third balancemass is provided, and wherein a fourth bearing is provided which movablysupports the third balance mass so as to be substantially free totranslate in the opposite direction of the third direction in order tocounteract a displacement of said one of the substrate table and sensorin said third direction.
 20. A system comprising: a lithographicapparatus comprising: an illumination system configured to condition aradiation beam; a support constructed to support a patterning device,the patterning device being capable of imparting the radiation beam witha pattern in its cross-section to form a patterned radiation beam; asubstrate table constructed to hold a substrate; and a projection systemconfigured to project the patterned radiation beam onto a target portionof the substrate; a metrology tool according to claim 1; and transfermeans for transferring substrates from the lithographic apparatus to themetrology tool.
 21. A system according to claim 20, wherein themetrology tool is integrated in or connected with the lithographicapparatus.
 22. A method for determining a parameter of a substrate,comprising the steps: providing a substrate with a pattern in alithographic apparatus; transferring the substrate from the lithographicapparatus to a substrate table of a metrology tool; and measuring aparameter of the substrate inside the metrology tool with a sensor;during which measuring, one of the substrate table and sensor isdisplaced with respect to the other one in at least a first direction,which displacement is counteracted with a translation of a balance massin the opposite direction.
 23. A method according to claim 22, whereinon displacement of said one of the substrate table and sensor withrespect to the other, the position of a combined center of gravity ofthe balance mass and said one of the substrate table and sensor relativeto the base frame also moves.
 24. A method according to claim 22,wherein, in use, vibration of the balance mass due to an elasticcoupling between the balance mass and the base frame is actively dampedby a balance mass actuator.